Heretofore various types of apparatus have been known which provide a means for determining the authenticity of paper securities or currency. Such apparatus utilize a photosensitive technique to operate on a given area of the security or paper currency, and depending on the results of the authentication tests performed, thereby determine the authenticity of the entire paper or note. In particular, standard apparatus test the cross hatch lines behind the portrait on U.S. currency or security. Of course, any of a number of patterns or arrangements could be so tested.
This generally consists of correlating the cross hatch lines or design pattern against a reference. Usually the reference consists of a reticle whereon is located a line pattern which corresponds to a specific currency note denomination or a specific security.
The reticle assembly and portrait are placed into relative movement while a light is passed through the paper and reticle. The relational position between the reticle and portrait is augmented and the light energy which passes through the paper is detected by a photosensitive cell or other detector. The relative movement between the reticle and the portrait background causes alignment and misalignment of the lines and allows for accurate measurement to be made respecting the authenticity of the background of the paper.
Referring more particularly to the figures depicting the prior art, FIG. 1 shows illustratively the cross hatch pattern 1 located in the background of portraits on some paper currency, particularly in the United States. The cross hatch pattern is comprised of vertical lines 2, horizontal lines 3 and resulting blocks 4. The line thickness and spacing between the lines is different for different currency denominations.
A reticle using only a vertical line reference pattern is shown generally as 5 in FIG. 2. The vertical lines 6 are located on a transparent lens 7. Another typical reticle is shown generally as 5' in FIG. 3. Diagonal reference lines 8 are located on lens 9. Diagonal reference lines 8 were used when photocopying resolution became good enough to copy both vertical and horizontal lines in cross hatch 1, FIG. 1, faithfully.
To date, all paper currency validation apparatus when built, possess the capability to test for the presence of only one currency denomination. This has necessiated the use of several validation apparatus wherever change or authentication is desired for various currency denominations. It has been thought that physical constraints would prohibit the inclusion of plural reticles into a single housing since the resolution required of the reticle masking would require a reticle of significant size and with sufficient lines to mask only valid patterns.